U.S. patent application number 12/715739 was filed with the patent office on 2010-06-24 for accurate capacitance measurement for ultra large scale integrated circuits.
This patent application is currently assigned to Taiwan Semiconductor Manufacturing Company, Ltd.. Invention is credited to Keh-Jeng Chang, Victor Chih Yuan Chang, Yih-Yuh Doong, Lien Jung Hung, Sally Liu, Yuh-Jier Mii.
Application Number | 20100156453 12/715739 |
Document ID | / |
Family ID | 40159631 |
Filed Date | 2010-06-24 |
United States Patent
Application |
20100156453 |
Kind Code |
A1 |
Doong; Yih-Yuh ; et
al. |
June 24, 2010 |
Accurate Capacitance Measurement for Ultra Large Scale Integrated
Circuits
Abstract
Test structures and methods for measuring contact and via
parasitic capacitance in an integrated circuit are provided. The
accuracy of contact and via capacitance measurements are improved
by eliminating not-to-be-measured capacitance from the measurement
results. The capacitance is measured on a target test structure
that has to-be-measured contact or via capacitance. Measurements
are then repeated on a substantially similar reference test
structure that is free of to-be-measured contact or via
capacitances. By using the capacitance measurements of the two test
structures, the to-be-measured contact and via capacitance can be
calculated.
Inventors: |
Doong; Yih-Yuh; (Hsin-Chu,
TW) ; Chang; Keh-Jeng; (Hsin-Chu, TW) ; Mii;
Yuh-Jier; (Hsin-Chu, TW) ; Liu; Sally;
(Hsin-Chu, TW) ; Hung; Lien Jung; (Taipei, TW)
; Chang; Victor Chih Yuan; (Hsin-Chu, TW) |
Correspondence
Address: |
SLATER & MATSIL, L.L.P.
17950 PRESTON ROAD, SUITE 1000
DALLAS
TX
75252
US
|
Assignee: |
Taiwan Semiconductor Manufacturing
Company, Ltd.
Hsin-Chu
TW
|
Family ID: |
40159631 |
Appl. No.: |
12/715739 |
Filed: |
March 2, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11966653 |
Dec 28, 2007 |
|
|
|
12715739 |
|
|
|
|
60947269 |
Jun 29, 2007 |
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Current U.S.
Class: |
324/762.01 ;
324/659 |
Current CPC
Class: |
G01R 31/2884 20130101;
H01L 2924/0002 20130101; G01R 31/2853 20130101; H01L 22/34
20130101; H01L 2924/0002 20130101; H01L 2924/00 20130101 |
Class at
Publication: |
324/765 ;
324/659 |
International
Class: |
G01R 31/26 20060101
G01R031/26; G01R 27/26 20060101 G01R027/26 |
Claims
1. A method of measuring parasitic capacitance in a semiconductor,
said method comprising: providing a first test structure comprising
a first conductive comb structure and a second conductive comb
structure complementary to the first comb, each of said first and
second conductive comb structures being formed in a first
interconnect layer, and a third conductive comb structure and a
fourth conductive comb structure complementary to the third comb,
each said third and fourth conductive comb structures being formed
in a second interconnect layer; wherein the first conductive comb
structure couples with the fourth conductive comb structure through
a first plurality of to-be-measured via formed at the cross-over
regions of the first and the fourth conductive comb structures, and
the second conductive comb structure couples with the third
conductive comb structure through a second plurality of
to-be-measured via formed at the cross-over regions of the second
and the third conductive comb structures; applying a first bias to
the first and the fourth conductive comb structures, and a second
bias to the second and the third conductive comb structures;
measuring a first capacitance on said first test structure between
said first bias and said second bias; providing a second test
structure comprising a fifth conductive comb structure and a sixth
conductive comb structure complementary to the fifth conductive
comb structure, both being formed in the first interconnect layer,
and a seventh conductive comb structure and an eighth conductive
comb structure complementary to the seventh conductive comb
structure, both being formed in the second interconnect layer;
wherein the fifth and the eight conductive comb structures are
substantially similar to the first and the fourth conductive comb
structures, respectively, being free of to-be-measured vias formed
between the fifth and the eight conductive comb structures; wherein
the sixth and the seventh conductive comb structures are
substantially similar to the second and the third conductive comb
structures, respectively, being free of to-be-measured vias formed
between the sixth and the seventh conductive comb structures;
applying the first bias to the fifth and the eight conductive comb
structures, and the second bias to the sixth and the seventh
conductive comb structures; measuring a second capacitance on the
second test structure between the first bias and the second bias;
and calculating a parasitic capacitance C.sub.v of to-be-measured
via using said first and said second capacitances.
2. The method of claim 1, wherein said first and second test
structures are formed on a semiconductor substrate comprising one
of doped silicon, silicon germanium, gallium arsenide, compound
semiconductor, multi-layers semiconductor, silicon on insulator
(SOI), and any combination thereof.
3. The method of claim 1, wherein said first and said second
plurality of to-be-measured via are through-silicon vias that
couple said first interconnect layer in a first integrated circuit
die with said second interconnect layer in a second integrated
circuit die overlying said first integrated circuit die.
4. The method of claim 1, wherein said calculating includes
deriving C.sub.v from capacitance measured on said first
capacitance (C.sub.T) and said second capacitance
(C.sub.T.sub.--.sub.ref) according to the formula
C.sub.v=(C.sub.T-C.sub.T.sub.--.sub.ref)/N, wherein N is the total
number of said first plurality and said second plurality of
to-be-measured vias in said first test structure.
5. The method of claim 1, wherein said steps of measuring said
first and said second capacitance is performed by a passive
capacitance measuring approach using at least an LCR meter.
6. The method of claim 1, wherein said step of measuring said first
capacitance and said second capacitance is performed by an active
capacitance measuring approach including a CBCM approach.
7. A test structure formed on an semiconductor substrate for
measuring the parasitic capacitance between a via and adjacent
conductive features of a semiconductor device, said test structure
comprising: a first conductive comb structure and a second
conductive comb structure complementary to the first comb
structure, each of said first and said second conductive comb
structures being formed in a first interconnect layer; a third
conductive comb structure and a fourth conductive comb structure
complementary to the third comb structure, each of said third and
said fourth conductive comb structures being formed in a second
interconnect layer; a first plurality of to-be-measured via formed
at the cross-over regions of said first conductive comb structure
and said fourth conductive comb structure, electrically coupling
said first conductive comb structure with said fourth conductive
comb structure; and a second plurality of to-be-measured via formed
at the cross-over regions of said second conductive comb structure
and said third conductive comb structure, electrically coupling
said second conductive comb structure with said third conductive
comb structure.
8. The test structure of claim 7, further comprising: a first probe
pad on a semiconductor substrate coupled to said first conductive
comb structure and said fourth conductive comb structure; and a
second probe pad on the semiconductor substrate coupled to said
second conductive comb structure and said third conductive comb
structure.
9. The test structure of claim 7, wherein said first and said
second conductive test structures are formed on a semiconductor
substrate comprising one of doped silicon, silicon germanium,
gallium arsenide, compound semiconductor, multi-layers
semiconductor, silicon on insulator (SOI), and any combination
thereof.
10. The test structure of claim 7, wherein first comb fingers of
said first conductive comb structure are substantially
perpendicular to fourth comb fingers of said fourth conductive comb
structure, and second comb fingers of said second conductive comb
structure are substantially perpendicular to third comb fingers of
said third conductive comb structure.
11. The test structure of claim 7, wherein said first and said
second plurality of to-be-measured via are through-silicon vias
that couple said first interconnect layer in a first integrated
circuit die with said second interconnect layer in a second
integrated circuit die overlying said first integrated circuit
die.
12. The test structure of claim 7, wherein said first and said
second plurality of to-be-measured vias have minimum design rule
size and maximum design rule density.
13. The test structure of claim 7, wherein a first comb handle of
said first conductive comb structure and a fourth comb handle of
said fourth conductive comb structure are connected by a first via,
and a second comb handle of said second conductive comb structure
and a third comb handle of said third conductive comb structure are
connected by a second via; wherein the first via is coupled to a
first bias through the first probe pad, and the second via is
coupled to a second bias through the second probe pads.
Description
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/966,653, entitled "Accurate Capacitance Measurement for
Ultra Large Scale Integrated Circuits," filed Dec. 28, 2007, which
application is hereby incorporated herein by reference.
CROSS-REFERENCE TO RELATED APPLICATIONS
[0002] This application relates to the following co-pending and
commonly assigned patent application Ser. No. 11/865,304 filed on
Oct. 1, 2007, entitled "Accurate Parasitic Capacitance Extraction
for Ultra Large Scale Integrated Circuits" (TSM07-0376), which
application is hereby incorporated herein by reference.
TECHNICAL FIELD
[0003] The present invention relates generally to techniques of
parametric measurements in an integrated circuit, and more
particularly, to on-chip test structures, and corresponding method
of measuring contact and via parasitic capacitance in a
semiconductor device.
BACKGROUND
[0004] As the density of integrated circuits continues to increase,
the scaling down of the semiconductor device feature sizes in
integrated circuits ("ICs") has followed. This trend poses
continuous technical challenges in manufacturing ICs with improved
performance. For example, it has been widely recognized that, when
device feature sizes shrink down to the ultra-deep submicron range
(less than 0.25 micron), interconnect (also generally referred to
as "net") delays between devices in an IC, due to parasitic
resistance/capacitance on the nets, begin to dominate the overall
time delay in an IC. As a consequence, significant efforts have
been taken by IC design engineers in extracting parasitic net
capacitance by improved accuracy so that IC designers can predict
the impact of the parasitic effects in an early design stage and
compensate for these detrimental effects through proper design
optimization steps.
[0005] Currently, extraction efforts are mainly focused on the
coupling capacitance between adjacent nets. Accurate models have
been developed for predicting time delays due to net-to-net
parasitic capacitance. However, the parasitic capacitance
associated with the contacts and vias, which are formed in an IC to
couple a net with a device node and to connect nets in different
interconnect layers, is either ignored or estimated with poor
accuracy. When the trend of device scaling in an IC continues, the
existing extraction methodology is problematic for various reasons.
Firstly, contact and via capacitance accounts for a significantly
increased proportion of the total interconnect delay in ICs made
with advanced technology, due to the reduced
contact-to-gate-electrode spacing and increased contact and via
density. Interconnect parasitic extraction ignoring parasitic
effects on contacts and vias may lead to significant discrepancy
between circuit simulation results and the actual circuit
performance.
[0006] Secondly, in existing parasitic extraction system, a
per-unit contact and via capacitance value derived from an ideal,
square-shaped contact and via primitive is typically used to
calculate the contact and via parasitic capacitance in an IC. The
aforementioned per-unit contact and via capacitance value is
typically calculated by a field solver, and the actual contact/via
shapes and size variations due to IC manufacturing process
variation are generally ignored. This may, in turn, lead to
inaccurate parasitic extraction on contacts and vias in an actual
IC. In existing practices, the contact-to-gate-electrode
capacitance in an IC is generally overestimated, while the
via-to-via capacitance in an IC is typically underestimated by a
margin of as large as about 10% in certain circumstances.
[0007] In view of the foregoing, it has become very important to
perform parasitic extraction in an IC with the actual contact/via
shapes and size variations in consideration. This is accomplished
through the invention fully described in the commonly assigned
patent application Ser. No. 11/865,304 filed on Oct. 1, 2007,
entitled "Accurate Parasitic Capacitance Extraction for Ultra Large
Scale Integrated Circuits" (TSM07-0376), which application is
hereby incorporated herein by reference. In the aforementioned
reference, contact and via capacitance models are developed for
contacts and vias occurring in an actual IC. Each contact and via
model possesses an ideal contact and via configuration (e.g.,
square shape without taped cross-sectional dimension) recognizable
by the existing extraction tools, while having a matching
capacitance with that of an actual contact and via. The capacitance
matching is performed through mapping an actual contact/via
configuration occurring in an IC into an ideal, square-shaped,
extracting-tool-recognizable contact/via configuration having an
"effective (contact/via) width." Using capacitance models thus
created, parasitic extraction on an IC in an existing extracting
system and the circuit simulation based there upon will match with
the actual performance of an IC. Nevertheless, creating the desired
contact and via models requires first and foremost making accurate
measurement of parasitic capacitance on contact and via that have
the shapes and size variations occurring in an actual IC.
[0008] FIG. 1 illustrates a schematic cross-section view of a known
test structure used in measuring contact-to-gate-electrode
capacitance C.sub.co.sub.--.sub.po on an MOSFET transistor
occurring in an IC. FIG. 1 shows one unit of interest on a
contact-to-gate-electrode capacitance test structure for clearer
view. In practice, a large number of units typically present in a
test structure in order to bring the capacitance of interest to a
measurable scale, since capacitance on a single unit is negligibly
small when compared to other capacitance components in an IC.
Contacts "c" are formed coupling a metal wire M1 in the first
interconnect layer with the source/drain regions "s" and "d,"
respectively. A known capacitance meter coupling to the gate
electrode "g" and one of the M1 wires is used to measure the
contact-to-gate-electrode capacitance, labeled as
C.sub.co.sub.--.sub.po in FIG. 1. However, this prior art test
structure and method of measuring C.sub.co.sub.--.sub.po suffer
from significant deficiencies because, besides the to-be-measured
contact-to-gate-electrode capacitance C.sub.co.sub.--.sub.po, the
gate-to-metal capacitance C.sub.g-m1, the junction capacitance
C.sub.gs, and the metal-to-metal capacitance C.sub.m1.sub.--.sub.m1
are inevitably introduced into the measurements.
SUMMARY OF THE INVENTION
[0009] These and other problems are generally solved or
circumvented, and technical advantages are generally achieved, by
embodiments of the present invention which provides test structures
and methods of making contact and via capacitance measurement with
improved accuracy.
[0010] In accordance with an embodiment of the present invention, a
method of measuring parasitic capacitance in a semiconductor is
provided. The method includes providing a first test structure
comprising a first conductive comb structure and a second
conductive comb structure complementary to the first comb, each of
said first and second conductive comb structures being formed in a
first interconnect layer, and a third conductive comb structure and
a fourth conductive comb structure complementary to the third comb,
each said third and fourth conductive comb structures being formed
in a second interconnect layer. The first conductive comb structure
couples with the fourth conductive comb structure through a first
plurality of to-be-measured via formed at the cross-over regions of
the first and the fourth conductive comb structures, and the second
conductive comb structure couples with the third conductive comb
structure through a second plurality of to-be-measured via formed
at the cross-over regions of the second and the third conductive
comb structures. The method further includes applying a first bias
to the first and the fourth conductive comb structures, and a
second bias to the second and the third conductive comb structures,
measuring a first capacitance on said first test structure between
said first bias and said second bias, and providing a second test
structure comprising a fifth conductive comb structure and a sixth
conductive comb structure complementary to the fifth conductive
comb structure, both being formed in the first interconnect layer,
and a seventh conductive comb structure and an eighth conductive
comb structure complementary to the seventh conductive comb
structure, both being formed in the second interconnect layer.
Further, the fifth and the eight conductive comb structures are
substantially similar to the first and the fourth conductive comb
structures, respectively, being free of to-be-measured vias formed
between the fifth and the eight conductive comb structures. The
sixth and the seventh conductive comb structures are substantially
similar to the second and the third conductive comb structures,
respectively, being free of to-be-measured vias formed between the
sixth and the seventh conductive comb structures. The method
further includes applying the first bias to the fifth and the eight
conductive comb structures, and the second bias to the sixth and
the seventh conductive comb structures, measuring a second
capacitance on the second test structure between the first bias and
the second bias, and calculating a parasitic capacitance C.sub.v of
to-be-measured via using said first and said second
capacitances.
[0011] In accordance with another embodiment of the present
invention, a method of a test structure formed on an semiconductor
substrate for measuring the parasitic capacitance between a via and
adjacent conductive features of a semiconductor device is provided,
said test structure comprising a first conductive comb structure
and a second conductive comb structure complementary to the first
comb structure, each of said first and said second conductive comb
structures being formed in a first interconnect layer. The test
structure further includes a third conductive comb structure and a
fourth conductive comb structure complementary to the third comb
structure, each of said third and said fourth conductive comb
structures being formed in a second interconnect layer. A first
plurality of to-be-measured via formed at the cross-over regions of
said first conductive comb structure and said fourth conductive
comb structure, electrically coupling said first conductive comb
structure with said fourth conductive comb structure is included. A
second plurality of to-be-measured via formed at the cross-over
regions of said second conductive comb structure and said third
conductive comb structure, electrically coupling said second
conductive comb structure with said third conductive comb structure
is also included.
[0012] An advantage of a preferred embodiment of the present
invention is that parasitic capacitance associated with contact and
via in an IC can be measured with substantially improved accuracy.
This is achieved by eliminating the effects of the
not-to-be-measured capacitances from the measurement results
through a first capacitance measurement on a target test structure
and a second capacitance measurement on a reference test structure.
Contact and via capacitance models created from there upon will
provide matching capacitances with the contacts and vias in an
actual IC.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] For a more complete understanding of the present invention,
and the advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which:
[0014] FIG. 1 illustrates a schematic cross-section view of a prior
art test structure used in measuring contact-to-gate-electrode
capacitance in an IC;
[0015] FIG. 2 illustrates a plan view of a portion of a testline
comprising contact and via capacitance test structures in preferred
embodiments;
[0016] FIG. 3 is a schematic layout view illustrating the
configuration of a DUT used for contact-to-gate-electrode
capacitance measurement in one preferred embodiment;
[0017] FIG. 4 shows a portion of a cross-sectional view of the DUT
in FIG. 3 in the area noted as C-C';
[0018] FIG. 5A is a layout view showing the contact configuration
in a unit cell of a target DUT for contact capacitance measurement
in a preferred embodiment;
[0019] FIG. 5B is a schematic cross-sectional view of DUT unit cell
in FIG. 5A in the area noted as D-D';
[0020] FIG. 6A is a layout view showing the contact configuration
in a unit cell of a reference DUT corresponding to the unit cell of
a target DUT described with respect to FIG. 5A;
[0021] FIG. 6B is a schematic cross-sectional view of the DUT unit
cell in FIG. 6A in the area noted as D-D';
[0022] FIG. 7A is a schematic layout view illustrating the
configuration of a target DUT used for via capacitance measurement
in one preferred embodiment;
[0023] FIG. 7B is an expanded view of the target DUT in FIG. 7A,
illustrating capacitances formed around one of to-be-measured via
under a preferred measurement condition;
[0024] FIG. 7C shows a reference via DUT in correspondence with the
target via DUT of FIG. 7A;
[0025] FIG. 7D is an expanded view of the reference DUT in FIG. 7C,
illustrating capacitances formed in a reference DUT under the same
measurement condition as that of a target DUT;
[0026] FIG. 7E shows an alternative target via DUT in
correspondence with the DUT in
[0027] FIG. 7A, having a reduced via density;
[0028] FIG. 8 illustrates a reference DUT and two target DUTs used
to measure and model via-to-metal capacitance in a preferred
embodiment;
[0029] FIG. 9 shows a perspective view of a prior art FinFET MOS
transistor;
[0030] FIGS. 10A and 10B illustrate schematic cross-sectional views
of a unit cell of a target DUT and a unit cell of a reference DUT
used to measure and model the contact capacitance in an IC
comprising FinFET MOS devices in a preferred embodiment;
[0031] FIG. 11 shows a portion of a cross-sectional view of a prior
art IC that includes multiple integrated circuit dies packaged in a
stacked manner; and
[0032] FIGS. 12A and 12B illustrate schematic cross-sectional views
of a target DUT and a reference DUT used to measure and model TSV
capacitance in an IC.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0033] The making and using of the presently preferred embodiments
are discussed in detail below. It should be appreciated, however,
that the present invention provides many applicable inventive
concepts that can be embodied in a wide variety of specific
contexts. The specific embodiments discussed are merely
illustrative of specific ways to make and use the invention, and do
not limit the scope of the invention.
[0034] The present invention will be described with respect to
preferred embodiments in a specific context, namely contact and via
capacitance test structures and methods of conducting contact and
via capacitance measurement in an IC. A common feature of the
various embodiments of the current invention is to eliminate the
not-to-be-measured capacitances from the measurement results
through proper design on test structures and measuring procedures.
Contact and via capacitance measurements made by preferred test
structures and methods result in significantly improved measurement
accuracy. As a result, contact and via capacitance models created
through the methods disclosed in the commonly assigned patent
application Ser. No. 11/865,304 filed on Oct. 1, 2007, entitled
"Accurate Parasitic Capacitance Extraction for Ultra Large Scale
Integrated Circuits" (TSM07-0376), can lead to a layout contact and
via parasitic capacitance extraction well matched with the
capacitance on an actual contact and via in an IC. The details of
the preferred embodiments will be described as the following.
[0035] FIG. 2 illustrates a plan view of a portion of testline 5
configured according to one embodiment of the present invention.
Testline 5 is formed on a semiconductor wafer substrate (not
shown), such as doped silicon, silicon germanium, gallium arsenide,
compound semiconductor, multi-layers semiconductor,
silicon-on-insulator (SOI), and any combination thereof. Testline 5
comprises a plurality of test structures 10 of various
configurations used in making accurate contact and via parasitic
capacitance measurements. Test structures 10 may be interchangeably
referred to as device-under-test (DUT) 10 throughout the following
description. Also shown in FIG. 2 is a serial number of aligned
test pads 15, such as P1, P2, and P3. Test pads 15 are formed with
metal or other electrically conductive materials using known
semiconductor processing techniques. Test pads 15 are electrically
coupled to DUTs 10, and are used to apply test stimuli to and
retrieve responses from selected DUTs 10. Test pads 15 may be
formed beside DUTs 10 (as shown) or above DUTs 10 through known
manufacturing processes. By studying and comparing the measured
capacitances on DUTs 10 of various contact and via configurations,
it is possible to obtain contact-to-gate-electrode and via
capacitance with improved accuracy and precision, which may, in
turn, lead to better contact and via models for accurate circuit
simulations.
[0036] FIG. 3 is a schematic layout view illustrating the
configuration of one type of DUT 10, namely 10A, used for
contact-to-gate-electrode capacitance measurement in one preferred
embodiment. As can be seen from FIG. 3, DUT 10A comprises an array
of DUT unit cells 20, each including active region 12 formed in a
semiconductor substrate (not shown), gate electrode 14 formed atop
active region 12, and conductive layer 16 formed in the first
interconnect layer (M1) overlying active region 12 and gate
electrode 14. In preferred embodiments, gate electrode 14 may be
formed by known gate electrode materials and processes, such as a
polysilicon layer formed and patterned over a gate dielectric
layer. M1 conductive layer 16 is electrically isolated from gate
electrode 14 and active region 12 by a first dielectric layer
ILD_I. An active region 12 is electrically isolated from an
adjacent active region 12 through isolation region 15 formed in the
substrate by known techniques, such as field isolation or shallow
trench isolation (STI). In a preferred embodiment, DUT 10A includes
a 100 by 100 array of unit cells 20, having a total number of unit
cells of 10,000.
[0037] DUT 10A also comprises two complementary conductive comb
structures "C.sub.L" and "C.sub.R," coupled to first test pad P1
and second test pad P2, respectively. "C.sub.L" and "C.sub.R" are
preferably formed by M1. Gate electrode 14 of each DUT unit cell 20
is electrically coupled to "C.sub.R" through contacts 18. M1
conductive layer 16 of each DUT unit cell 20 is electrically
coupled to comb structure "C.sub.L." When M1 is used to make comb
structure "C.sub.L," "C.sub.L" and conductive layer 16 may be
formed by common known process steps. DUT 10A further comprises
active region 23 formed along the edges of DUT 10A, coupled to
third test pad P3. Active region 23 and active region 12 have a
similar conductivity and may be formed simultaneously through
common known process steps. Moreover, active region 23 and active
region 12 of each DUT unit cell 20 are electrically connected
together through contacts 18 presented between active regions 12,
23, and the M1 fingers of comb structure "C.sub.L," as shown.
[0038] FIG. 4 shows a portion of a cross-sectional view of DUT 10A
in the area noted as C-C' in FIG. 3, further illustrating the
various features described above. It can be seen that, in the
region of DUT unit cell 20, conductive layer 16 and active region
12 are electrically connected through contacts 18, but isolated
from gate electrode 14 through ILD_I and gate dielectric layer 11.
Further, active regions 12 in the DUT array region and active
region 23 along the DUT edge are electrically connected through M1
conductive layer 16 and contacts 18.
[0039] FIG. 5A is an expanded layout view showing, among other
features, the contact configuration in DUT unit cell 20 of DUT 10A
as described above with respect to FIG. 3. For clearer view, M1
layers overlying gate electrode 14 and active region 12 are not
shown. FIG. 5A reveals that contacts used in making electrical
connections between the various conductive features in DUT unit
cell 20 comprise three major groups. The first contact group
comprises contacts 18a that couple gate electrode 14 to M1 finger
(see FIG. 3) of comb structure "C.sub.R." The second contact group
comprises contacts 18b that connect active region 12 to M1 finger
of comb structure "C.sub.L." Contacts 18a and 18b are primarily
used in making electrical connections between gate electrode 14 and
test pad P2, and between active region 12 and test pad P1,
respectively (see FIG. 3). Thus, the sizes and configurations of
contacts 18a and 18b are less significant and should not be limited
to those shown in FIG. 5A, so long as contacts 18a and 18b provide
desired electrical connections as described above.
[0040] The third contact group comprises contacts 18c that are
formed between active region 12 and M1 conductive layer 16. Contact
18c are aligned with and evenly distributed along both sides of
gate electrode 14. Preferably, contacts 18c are used to model the
contacts that are actually occurring in an IC. Thus, the contact
size, contact density and contact-to-gate-electrode spacing of
contacts 18c are representative of those that are used in
connecting MOSFET (Metal-Oxide-Silicon Field Effect Transistor)
devices in an actual IC product. In preferred embodiments, a DUT
having a contact or via to be modeled and measured is also
generally referred to as a target DUT, or a target test
structure.
[0041] In FIG. 5A, the size of each of contacts 18c has a minimum
design rule size in correspondence with a certain technology
generation. The contact density (typically measured in
contact-to-contact spacing) and contact-to-gate electrode spacing
of contacts 18c have the maximum design rule contact density and
minimum design rule contact-to-gate-electrode spacing,
respectively. This contact configuration is representative of the
vast majority of contact configurations used in an actual IC. In
order to model other contact configurations used in an IC, contacts
18c may also have a contact density and contact-to-gate-electrode
spacing that are, for example, multiple of the minimum design rule
contact-to-contact and contact-to-gate-electrode spacing,
respectively.
[0042] FIG. 5B is a schematic cross-sectional view of DUT unit cell
20 in FIG. 5A in the area noted as D-D.' It is noted that M1
conductive layer 16 omitted in FIG. 5A is shown herein. FIG. 5B
includes the electrical connections making into the various
conductive regions of DUT unit cell 20 when making desired
C.sub.co-po measurements in preferred embodiments. Also illustrated
in FIG. 5B are parasitic capacitances in DUT unit cell 20 when it
is under preferred measurement conditions.
[0043] The method of making desired C.sub.co-po measurement will
now be described with respect to FIG. 5B. It is shown in FIG. 5B
that, when making C.sub.co-po measurement in preferred embodiments,
test pads P1 and P3 are coupled to drive (high) end 24 of a known
LCR (inductance-capacitance-resistance) meter 50, having a first DC
voltage bias. Test pad P2 is coupled to sense (low) end 26 of LCR
meter 50, having a second DC voltage bias. Under this bias
condition, conductive layer 16, contacts 18 and active region 12
are electrically equivalent and have a first DC bias, while gate
electrode 14 having a second bias. Capacitances between these
conductive features include M1-to-gate-electrode capacitance
C.sub.m1-po, contact-to-gate-electrode capacitance C.sub.co-po on
both sides of gate electrode 14, and active-to-gate-electrode
capacitance C.sub.act-po on both sides of gate electrode 14. It is
noted, however, that dividing C.sub.act-po into a symmetric left
and right component, as shown in FIG. 5B, is made for the
convenience of the device modeling. However, in practice, it is a
single capacitance formed between active region 12 and gate
electrode 14 under the current measurement condition. The
capacitances measured under the current measurement configuration
include the lump sum of C.sub.m1-po, C.sub.co-po, and C.sub.act-po
in DUT unit cell 20. The total capacitance C.sub.A measured on DUT
10A of FIG. 3 between the two probes of LCR meter 50 can be
expressed as the following:
C.sub.A=N(C.sub.m1-po+C.sub.co-po+C.sub.act-po+C.sub.extra)+C.sub.other
(1)
where N represents the total number of DUT unit cells 20 in DUT
10A; C.sub.extra includes the capacitance in DUT unit cell 20 other
than C.sub.m1-po, C.sub.co-po, and C.sub.act-po, such as parasitic
capacitance between contacts 18b (see FIG. 5A) and gate electrode
14; And C.sub.other includes, for example, any other capacitance
associated with the conductive paths between capacitance meter
probe tips and DUT unit cells 20, such as parasitic capacitance on
comb structures "C.sub.L," "C.sub.R", and test pads P1, P2, and
P3.
[0044] It is herein stressed, although a known passive capacitance
measuring approach using an LCR meter is described in the example
with respect to FIG. 5B, other suitable capacitance measuring
approaches can also be employed to measure the contact and via
capacitance of interest without departing from the spirit and scope
of the invention. In an additional and/or alternative embodiment, a
known active capacitance measuring approach, such as the well-known
CBCM (charged-based capacitance measurement) approach is also used
for the desired contact capacitance measurement. In other
embodiments, known capacitance measurement approaches, such as the
above described LCR meter approach, CBCM approach, and other
suitable active or passive capacitance measurement approaches are
used to measure via capacitance in an IC. In preferred embodiments,
there is no preference between the various available capacitance
measuring approaches so long as desired measuring accuracy and
precision is achieved.
[0045] Afterwards, the measurement just described is repeated on a
reference contact-to-gate-electrode capacitance test structure
(DUT) formed, for example, on a same test line. The reference DUT
is substantially similar to target DUT 10A illustrated above with
respect to FIG. 3, except that the contact configuration in DUT
unit cells of a reference DUT does not include the contacts to be
modeled.
[0046] FIG. 6A is a layout view illustrating DUT unit cell 21 of a
reference contact-to-gate-electrode capacitance test structure
mentioned above. To clarify description and avoid repetition,
numerals and letters used in FIG. 5A are used again for the various
elements in FIG. 6A. Like FIG. 5A, M1 layers overlying gate
electrode 14 and active region 12 are not shown for clearer view.
Also, reference numbers described in FIG. 5A are not described
again in detail herein. It is shown in FIG. 6A that DUT unit cell
21 is identical to DUT unit cell 20 in FIG. 5A, except that
contacts 18c in DUT unit cell 20 of target DUT 10A no longer exist
in DUT unit cell 21 of a reference DUT.
[0047] FIG. 6B is a schematic cross-sectional view of DUT unit cell
21 in FIG. 6A. The cross-sectional view of FIG. 6B is made at the
same area D-D' as that made at DUT unit cell 20 in FIG. 5A. To
clarify description and avoid repetition, the reference numbers,
numerals, letters, and measurement setup described with respect to
FIG. 5B are re-used in FIG. 6B. The areas taken by contacts 18c of
DUT unit cell 20 in FIG. 5B are drawn in ghost lines in FIG. 6B for
comparison purposes. These areas are filled with ILD_I in DUT unit
cell 21.
[0048] When the same measurement described with respect to target
DUT 10A in FIG. 3 is repeated on the reference DUT described with
respect to FIG. 6B, the total capacitance C.sub.B measured on
reference DUT between the two probes of capacitance meter 50 can be
expressed as the following:
C.sub.B=N(C.sub.m1-po+C.sub.act-po+C.sub.extra)+C.sub.other (2)
Subsequently, the to-be-measured C.sub.co-po can be derived from
C.sub.A and C.sub.B as the following:
C.sub.co-po=(C.sub.A-C.sub.B)/N (3)
In preferred embodiments, C.sub.co-po is typically expressed in a
capacitance-per-length format. In one preferred embodiment,
C.sub.co.sub.--.sub.po obtained through above measurement steps has
a value of about 2.96E-2 (fF/.mu.m). In another preferred
embodiment, C.sub.co.sub.--.sub.po obtained on similar target and
reference DUTs has a value of about 3.06E-2 (fF/.mu.m). This
provides a highly accurate measurement of C.sub.co-po, because the
unwanted capacitances are excluded from the measurement result
through the two-steps measurement procedure as described above.
[0049] It is worthy noting, however, that, in practice,
M1-to-gate-electrode capacitance in DUT unit cell 21 in a reference
DUT is typically not identical to that of DUT unit cell 20 in a
target DUT under a same measurement condition. Thus, the validity
of deriving C.sub.co-po from C.sub.A and C.sub.B should be analyzed
and verified. As shown in FIG. 6B, M1-to-gate-electrode capacitance
in DUT unit cell 21 is slightly larger than C.sub.m1-po by an
additional value of C.sub.i, due to the regained spaces in ILD_I,
which are otherwise occupied by contacts 18c in a target DUT.
Similarly, active-to-gate-electrode capacitance in DUT unit cell 21
is slightly larger than C.sub.act-po by an additional value of q,
as shown. But, as those skilled in the art will recognize, C.sub.i
and C.sub.j, associated with a single contact, are negligibly small
by nature because the space gained from a to-be-modeled contact,
which typically has a minimum design rule contact size, is
extremely small in advanced technology.
[0050] In preferred embodiments, additional caution has also been
taken to reduce the accumulative effects of Ci and Cj. As an
example, when constructing contact test structures, the total
numbers of to-be-measured contacts in a target DUT are limited so
that the accumulation of C.sub.i and C.sub.j will not cause
significant discrepancy between M1-to-gate-electrode capacitances
in a target and reference DUT. In a preferred embodiment, a target
DUT for contact-to-gate-electrode capacitance measurement has a
unit cell array of 100 by 100, each DUT unit cell having ten
contacts to be modeled and measured. Additionally, in order to
obtain a good statistical result of C.sub.co-po measurement, same
measurement is repeated on a number of target DUTs that have the
same configurations but different numbers of
contacts-to-be-measured in their DUT unit cells. For example, in
the aforementioned embodiment, the same measurement is repeated on
a second target DUT that has a 100 by 100 unit cell array, but only
five to-be-measured contacts in each unit cell. This practice is
routinely used in preferred embodiments and is generally referred
to as DUT split.
[0051] The contact-to-gate-electrode capacitance measurement
results may then be used to create more accurate contact models
that may be used by Electronic Design Automation (EDA) tools. The
contact models thus created have a capacitance that matches with
the contact capacitance in an actual IC. This may, in turn, lead to
more accurate IC simulation results. The method of creating contact
models using the measurement results from preferred embodiments of
the current invention can be found in commonly assigned and
co-pending U.S. patent application Ser. No. 11/865,304 filed on
Oct. 1, 2007, and entitled "Accurate Parasitic Capacitance
Extraction for Ultra Large Scale Integrated Circuits," which
application is incorporated herein by reference.
[0052] The second aspect of this invention relates to via
capacitance test structures and methods of conducting accurate via
capacitance measurement in an IC. The inventive features of via
test structures and methods of conducting via capacitance
measurement are similar to those described above in regard to
contact test structures and methods of measuring contact
capacitance. Through studying and comparing via capacitance
measurement results on target DUTs and a reference DUT, accurate
via capacitance may be obtained by eliminating the
not-to-be-measured capacitances in the measurement results. The
details of the preferred embodiments will be described as the
following.
[0053] FIG. 7A is a schematic layout view illustrating the
configuration of target DUT 10B, used for via capacitance
measurement in one preferred embodiment of the present invention.
Target DUT 10B comprises a first conductive comb structure C1,
having downward fingers and a second complementary conductive comb
structure C2, having upward fingers. C1 and C2 are electrically
isolated from each other and are preferably made in a first
interconnect layer, such as M1. Target DUT 10B also comprises a
third conductive comb structure C3, having rightward fingers and a
fourth complementary conductive comb structure C4, having leftward
fingers. C3 and C4 are electrically isolated from each other and
are formed in an upper interconnect layer, such as M2. M1 and M2
are electrically insulated from each other by a first inter-metal
dielectric layer (not shown), such as silicon dioxide, as is well
known in the art. Moreover, C1 is electrically coupled with C4
through to-be-measured-and-modeled vias 40a (empty circles) formed
at C1-C4 cross-over regions and at the end of the "handles" of
combs C1 and C4. In FIG. 7A, the end spot of the "handles" of C1
and C4 is highlighted with an "A" within a dashed circle for
clearer view. It should be noted that the dashed circles around
points "A" and "B" are not a structural element, but are used only
to visually highlight the locations of points "A" and "B." In a
similar manner, C2 is electrically coupled with C3 through vias 40b
(solid circles) at C2-C3 cross-over regions and at the end spot "B"
of the handles of combs C2 and C3. Vias 40b are typically
substantially similar to vias 40a. Contacts 40a and 40b are
preferably formed by common processing steps. Nodes "A" and "B" may
be, in turn, connected to probe pads (not shown) on a testline,
where test stimuli may be applied. It is worthy noting that, under
the current DUT configuration, vias 40a are electrically connected
to node "A," and vias 40b are electrically connected to node "B."
In a preferred embodiment, vias 40a and 40b on target DUT 10B have
a maximum design rule density.
[0054] Remaining in FIG. 7A, when conducting via capacitance
measurements on target DUT 10B, a known LCR meter 50 is connected
between node "A" and node "B" through corresponding probe pads on a
test line (not shown). In one preferred embodiment, drive end 24 of
LCR meter 50 is coupled to node "A" and sense end 26 of LCR meter
50 is coupled to node "B." As a result, vias 40a are connected to a
first DC bias V1 and vias 40b are connected to a second DC bias
V2.
[0055] FIG. 7B is an expanded view of target DUT 10B in FIG. 7A,
illustrating capacitances formed around one of vias 40a under the
current DC bias condition. It is shown that the capacitances
include via capacitances C.sub.v between via 40a and surrounding
conductive features connected to ground, and Metal-to-Metal
capacitances C.sub.m. It is noted that C.sub.v typically includes
via-to-via, via-to-M1, and via-to-M2 capacitance. In the current
embodiment, these components are not separately measured and
modeled, and thus, are not separately shown in FIG. 7B in order to
simplify illustration. For clearer description, a combined C.sub.v
and C.sub.M will be used herein to represent the overall via
capacitance and Metal-to-Metal capacitance measured on target DUT
10B under a preferred measurement condition.
[0056] The total capacitance C.sub.T measured from DUT 10B of FIG.
7A between the drive end 24 and sense end 26 of LCR meter 50 can be
expressed as the following:
C.sub.T=C.sub.v+C.sub.M+C.sub.other (4)
where C.sub.other represents capacitances on DUT 10B, other than
C.sub.v and C.sub.M, under a preferred measurement condition.
[0057] Subsequently, the above measurement is repeated on a
reference via capacitance DUT. The reference DUT for via
capacitance measurement is substantially similar to target via DUT
10B illustrated above with respect to FIG. 7A, except that the vias
40a and 40b in the cross-over regions are removed, only leaving the
ones at spots "A" and "B." A reference via test structure
10B.sub.ref in correspondence with target via DUT 10B of FIG. 7A is
shown in FIG. 7C.
[0058] FIG. 7D is an expanded view of reference DUT 10B.sub.ref in
FIG. 7C, illustrating capacitances formed in DUT 10B.sub.ref under
the same measurement condition as that of target DUT 10B in FIG.
7A. It is shown that via capacitances no longer exist, only leaving
the Metal-to-Metal capacitances C.sub.m. The total capacitance
C.sub.T.sub.--.sub.ref measured from DUT 10B.sub.ref of FIG. 7C
between node "A" and "B" can be expressed as the following:
C.sub.T.sub.--.sub.ref=C.sub.M+C.sub.other (5)
the to-be-measured via capacitance C.sub.v can be derived from
C.sub.T and C.sub.T.sub.--.sub.ref as the following:
C.sub.v=(C.sub.T-C.sub.T.sub.--.sub.ref)/N (6)
where N represents the total number of to-be-measured vias in a
target via DUT, such as 40a of DUT 10B in FIG. 7A. C.sub.v is
typically expressed in a capacitance-per-length format.
[0059] In preferred embodiments, the practice of DUT split, used in
obtaining accurate contact-to-gate-electrode capacitance as
described earlier, is also conducted in measuring via capacitance.
As an example, FIG. 7E shows a via target DUT 10B1 having a reduced
via density, when compared with its counterpart DUT 10B illustrated
in FIG. 7A. Similarly, the numbers of to-be-measured vias in a
target DUT is limited for the same rationale explained earlier as
with contact capacitance DUT. In the current embodiment, target via
DUT 10B of FIG. 7A has about 226,000 vias, and target via DUT 10B1
of FIG. 7E has about 9,000 vias. Through via capacitance
measurement in preferred embodiments, it is revealed that via
capacitance can account for about 15% of the overall
interconnect-related capacitance in an IC product made by advanced
technology. This further justifies the criticality of creating
accurate via models in order to obtain accurate simulation results
in ICs made by advanced technology.
[0060] FIG. 8 illustrates another preferred embodiment of the
current invention, where similar test structures and measurement
steps described above are used to study the effect on via
capacitance due to the feature size variation of conducting layers
surrounding a via. The structure of the reference DUT is
substantially similar to that used for via capacitance measurement
as described with respect to FIG. 7C, except that vias 40a are
presented at the cross-over regions of comb structures C1 and C2.
When the same measurement condition described above is applied to
the reference DUT of the current embodiment, the total capacitance
measured between node "A" and "B" can be expressed as the
following:
C.sub.ref=C.sub.via.sub.--.sub.ref+C.sub.M+C.sub.other (7)
where C.sub.via.sub.--.sub.ref is the total via capacitance in the
reference DUT, formed between 40a and adjacent M1 and M2 fingers
connected to ground; C.sub.M is the total Metal-to-Metal
capacitance formed in the reference DUT between metal layers
connected to the drive end 24 having first bias V1 and the sense
end 26 having a second bias V2 (see FIG. 7C); And C.sub.other
represents capacitances associated with the reference DUT, other
than C.sub.via and C.sub.M.sub.--.sub.ref, such as the capacitance
on test pads and capacitance meter probe tips, as described
earlier.
[0061] FIG. 8 also shows a first and a second target test
structures DUT_I and DUT_II. DUT_I differs from the reference DUT
in that fingers 28 of conductive comb structure C2 in the first
interconnect layer (e.g., M1) are significantly thinner than those
of the reference DUT. DUT_II differs from the reference DUT in that
fingers 29 of conductive comb structure C3 in the second
interconnect layer (e.g., M2) are significantly thinner than those
of the reference DUT. As can be appreciated, when the same
measurement condition is applied on DUT_I, the total capacitance
C.sub.DUT.sub.--.sub.I measured between node "A" and "B" can be
expressed as the following:
C.sub.DUT.sub.--.sub.I=C.sub.via.sub.--.sub.DUT.sub.--.sub.I+C.sub.M+C.s-
ub.other (8)
where C.sub.via.sub.--.sub.DUT.sub.--.sub.I is the total via
capacitance in the target DUT_I. Because the width of M1 fingers 28
of conductive comb C2 is significantly reduced,
C.sub.via.sub.--.sub.DUT.sub.--.sub.I is expected to be
significantly smaller than C.sub.ref due to reduced via-to-M1
capacitance. Meanwhile, the smaller width of M1 fingers 28 of C2
will have less impact on the total Metal-to-Metal capacitance
because the spacing and area between M1 fingers 28 of C2 and M1
fingers of C1 remains unchanged, while capacitance change between
M1 fingers 28 of C2 and upper layer M2 fingers is negligibly small,
as can be appreciated by those skilled in the art. By comparing
C.sub.ref and C.sub.DUT.sub.--.sub.I, it is possible to create a
via model having an improved accuracy of via-to-Metal
capacitance.
[0062] Similarly, the total capacitance C.sub.DUT.sub.--.sub.II
measured between node "A" and "B" on target DUT II can be expressed
as the following:
C.sub.DUT.sub.--.sub.II=C.sub.via.sub.--.sub.DUT.sub.--.sub.II+C.sub.M+C-
.sub.other (9)
because the width of M2 fingers 29 of conductive comb C3 is
significantly reduced, C.sub.via.sub.--.sub.DUT.sub.--.sub.II is
expected to be significantly smaller than C.sub.ref due to reduced
via-to-M2 capacitance, while the changes on the total
Metal-to-Metal capacitance is negligibly small, due to similar
reasons explained above. Thus, it is possible to create a via model
having an improved accuracy of via-to-M2 capacitance.
[0063] In a further embodiment of the current invention, the
preferred contact and via capacitance test structures and methods
of conducting contact and via capacitance measurement described
above are used in measuring and modeling contact capacitance in IC
products made of semiconductor devices having a three-dimensional
(3-D) configuration, such as a FinFET.
[0064] FIG. 9 shows a perspective view of a prior art FinFET MOS
transistor 30. As is known in the art, FinFET MOS device 30 has a
3-D configuration when compared with the conventional planar MOS
device configuration. FinFET structures are known as promising
candidates for MOS devices in advanced technology because their
configuration is known to suppress short channel effects and
maintain desired drive current when the device dimension scales
down to the nanometer range. In FIG. 9, FinFET MOS transistor 30,
fabricated on an insulating substrate 35, includes silicon source
island 40 and drain island 42 connected by a silicon fin (channel)
44. Gate region 46 extends across channel fin 44 and is isolated
from channel fin 44 by gate oxide 48. Channel fin 44 extends
horizontally on substrate 35 with gate 46 in planes on either side
of channel fin 44. Contacts 52 are formed between source/drain
islands 40, 42, gate region 46, and the first interconnect layer
(not shown).
[0065] FIGS. 10A and 10B illustrate schematic cross-sectional views
of DUT unit cell 36 of a target DUT (not shown) and DUT unit cell
37 of a corresponding reference DUT (not shown) constructed in a
preferred embodiment to measure and model the contact capacitance
in an IC comprising FinFET MOS devices. The configurations of the
DUTs and methods of conducting the desired capacitance measurements
thereon are similar to those described previously with respect to
DUTs used in measuring and modeling the contact-to-gate-electrode
capacitance in ICs made of planar MOS devices, except that DUTs in
the current embodiment are formed by processing steps used in
forming ICs comprising FinFET devices. It is shown in FIG. 10A that
contacts 18c are formed to couple source/drain islands 40, 42 with
conductive layer 16, preferably in the first interconnect layer M1.
Conductive layer 16 and gate electrode 46 of each DUT unit cell 36
are, in turn, connected to a first and a second probe pads on a
testline (not shown). When conducting desired capacitance
measurements, a known LCR meter 50 is coupled between the first and
second probe pads. The first probe pad is biased to a first DC
voltage V1 and the second probe is biased to a second DC voltage
V2. LCR meter 50 reads the total capacitance, including
to-be-measured contact-to-gate-electrode capacitance
C.sub.co.sub.--.sub.po, on the target DUT.
[0066] The measurement is repeated on a reference DUT, which is
substantially similar to the target DUT, except to-be-measured
contacts 18c are removed from the reference DUT unit cells. The
method of making measurements on a reference DUT, and the procedure
of deriving C.sub.co.sub.--.sub.po from the measurement results on
the target and reference DUTs are similar to those described
previously in regard to ICs made of planar devices. Furthermore,
the measures taken to reduce measurement errors, such as the DUT
split described earlier, are also used in the current embodiment,
and will not be described again.
[0067] In an additional embodiment of the current invention, via
capacitance test structures and methods of measuring the same are
developed to measure and model through-silicon-via (TSV)
capacitance in an IC product that encapsulates multiple integrated
circuit dies configured in a stacked manner.
[0068] FIG. 11 shows a portion of a cross-sectional view of a
typical IC product 51, which includes multiple integrated circuit
dies packaged in a stacked manner. This stacked package scheme is
known to provide a space-saving solution for forming a complex
electronic system in a single package through stacking multiple
integrated circuit dies. IC product 51 includes a first die 55, a
second die 60, and a third die 65, one stacking on the top of the
other, as shown. In a preferred embodiment, dies 60 and 65 are
bulky, silicon-based integrated circuits having a thin silicon
substrate of about 100 .mu.m, for example. Die 55 is a bulky,
silicon-based integrated circuit, but has a thick silicon substrate
of about 1000 .mu.m, which provides mechanical support for dies 60
and 65. In other preferred embodiments, dies 55, 60, and 65 may
include integrated circuits having other substrate materials and
configurations, such as silicon germanium, gallium arsenide,
compound semiconductor, multi-layers semiconductor,
silicon-on-insulator (SOI), and any combination.
[0069] Remaining in FIG. 11, dies 55, 60, and 65 are electrically
insulated from each other through dielectric glue layers 53.
Moreover, TSVs 45 are formed in the silicon substrates of dies 60
and 65, through known processing techniques, to provide electrical
connections between interconnect layers M in an underlying die to
interconnect layers M in an overlying die, as shown. As a common
feature, TSVs 45 are typical larger than a conventional via and, in
general, have higher aspect ratio (depth-to-width ratio). As can be
appreciated, when circuit density in an IC continues to increase in
advanced technology, parasitic capacitance C.sub.v between adjacent
TSVs 45, and between TSVs 45 and surrounding metal layers M having
different electrical potential may become significantly large.
Thus, in order to predict the circuit performance of IC product 51,
accurate measuring and modeling of the parasitic capacitance
associated with TSVs have become increasingly important.
[0070] The TSV test structures and methods of measuring the same in
the current embodiment are similar to those described above with
respect to FIGS. 7A-7E, where the to-be-measured vias are
conventional ones formed in a dielectric layer, such as a silicon
dioxide layer, connecting lower and upper interconnect layers over
a die area of an IC. In contrast, TSV test structures of the
current embodiment are formed by processing steps similar to those
used in forming ICs having multiple dies in a stacked manner.
[0071] FIG. 12A illustrates a portion of a schematic
cross-sectional view of a target TSV DUT 70 in a preferred
embodiment. Target TSV DUT 70 includes metal wires 57 formed in
dielectric layer ILD_I of first die 55. Target TSV DUT 70 also
includes metal wires 58 formed in dielectric layer ILD_II of second
die 60. Die 60 stacks atop die 55, and is bonded to die 55 through
thin dielectric glue layer 53. TSVs 45 pass through dielectric glue
layer 53, silicon substrate 61 and ILD_II of second die 60,
connecting metal wires 57 of die 55 to metal wires 58 of die 60. DC
biases similar to those described previously are applied to
to-be-measured TSVs 45 and surrounding metal wires 57 and 58.
Parasitic capacitances, such as via capacitance C.sub.v and
metal-to-metal capacitance C.sub.m, formed under the preferred
measurement condition are shown in FIG. 12A. The total capacitance
on target TSV DUT 70 can be measured through similar measurement
setup described earlier.
[0072] The measurement is repeated on reference TSV DUT 71, as
shown in FIG. 12B. Reference TSV DUT 71 is substantially similar to
target TSV DUT 70 just described, except to-be-measured TSVs 45 are
removed in reference TSV DUT 71. It is shown in FIG. 12B that,
under similar bias conditions, via capacitances C.sub.v no longer
exist in reference TSV DUT 71. The method of making capacitance
measurements on target and reference TSV DUTs, and the procedure of
deriving desired via capacitance from the measurement results are
substantially similar to those described previously in regard to
ICs made of conventional vias. Furthermore, the measures taken to
reduce measurement errors, such as DUT split described earlier, are
also used in the current embodiment, and will not be described
again.
[0073] Although the present invention and its advantages have been
described in detail, it should be understood that various changes,
substitutions and alterations can be made herein without departing
from the spirit and scope of the invention as defined by the
appended claims. For example, the via capacitance test structures
and methods of making the desired measurement are disclosed through
embodiments having vias formed between the first and the second
interconnect layer in an IC. It can be well appreciated that the
inventive features can be readily used in making capacitance
measurement on vias between any two different interconnect layers
in an IC. As another example, the configurations of the various
DUTs used in the preferred embodiments should not be limited to
those disclosed above. Other DUT configurations suitable for making
the desired measurement should be within the scope of the current
invention so long as the following inventive features are present.
First, a target contact or via DUT includes a large number of
duplicate to-be-measured contact or via so that the aggregate
capacitance can be measured with desired precision. Secondly, a
reference DUT and a target DUT are substantially similar, except
the to-be-measured contact or via are removed from the reference
DUT. And thirdly, a to-be-measured contact or via capacitance can
be extracted from measurement results on a reference DUT and a
target DUT.
[0074] Moreover, the scope of the present application is not
intended to be limited to the particular embodiments of the
process, machine, manufacture, composition of matter, means,
methods and steps described in the specification. As one of
ordinary skill in the art will readily appreciate from the
disclosure of the present invention, processes, machines,
manufacture, compositions of matter, means, methods, or steps,
presently existing or later to be developed, that perform
substantially the same function or achieve substantially the same
result as the corresponding embodiments described herein may be
utilized according to the present invention. Accordingly, the
appended claims are intended to include within their scope such
processes, machines, manufacture, compositions of matter, means,
methods, or steps.
* * * * *